Image reading apparatus

ABSTRACT

An image reading apparatus includes a conveyance unit configured to convey an original; a reading unit comprising a reading sensor, the reading sensor having a light receiving element to receive light of a first color and a light receiving element to receive light of a second color that is different from the first color, wherein the reading unit is configured to read an image of the original conveyed by the conveyance unit by using the reading sensor to generate image data which represents a reading result of the reading unit; at least one processor configured to: determine a first abnormal position that is a position in a first direction of an abnormal pixel of the first color in an image represented by the image data.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to an image reading apparatus which readsan image of an original.

Description of the Related Art

An image reading apparatus having a configuration in which documentsstacked on an original tray are read one by one by an auto documentfeeder (hereinafter referred to as “ADF”) is known. Japanese PatentApplication Laid-open No. 2001-285595 discloses such an image readingapparatus. In this image reading apparatus, the ADF conveys the documentso as to pass over the platen arranged at a reading position of theimage reading apparatus. The image reading apparatus irradiates theoriginal passing over the platen with light from a light source, then,the image reading apparatus receives the reflected light by an imagepickup element to convert it into an electrical signal to thereby readthe image of the original.

Opportunities to read and digitize images of forms, such as invoices,using the image reading apparatus are increasing. In order to digitizemany forms, there is an increasing demand for feeding forms using theADF. When the original is fed using the ADF, dust (foreign matter), suchas paper dust caused by the original itself or toner peeled off from theoriginal, may adhere to the platen which is arranged at a readingposition. When reading the image with the foreign matter on the platen,the irradiation light and the reflected light are blocked by the foreignmatter. Thus, a vertical line (streak image) appears at a position ofthe foreign matter in an image (reading image). In many cases, the imagereading apparatus has a streak image correcting function for erasingsuch streak images.

When the streak image overlaps with a character on the original, thecharacter in the reading image may also be erased by the streak imagecorrection. Especially when reading the image such as the form, erasingof the character is causes unfavorable results for the user. However, ifthe streak image correction is not performed at all, the streak imageremains in the reading image, which makes it difficult for the user torecognize characters from the reading image. Therefore, in view of theabove-mentioned problems, the present disclosure provides the imagereading apparatus that appropriately corrects the streak image caused bythe foreign matter on the reading position.

SUMMARY OF THE INVENTION

The image reading apparatus according to the present disclosureincludes: a conveyance unit configured to convey an original; a readingunit comprising a reading sensor, the reading sensor having a lightreceiving element to receive light of a first color and a lightreceiving element to receive light of a second color that is differentfrom the first color, wherein the reading unit is configured to read animage of the original conveyed by the conveyance unit by using thereading sensor to generate image data which represents a reading resultof the reading unit; at least one processor configured to: determine afirst abnormal position that is a position in a first direction of anabnormal pixel of the first color in an image represented by the imagedata, wherein, in the image represented by the image data, the firstdirection is a direction which intersects a second directioncorresponding to a conveyance direction in which the original isconveyed; determine a second abnormal position that is a position in thefirst direction of an abnormal pixel of the second color in the imagerepresented by the image data; perform correction processing forremoving the streak image by correcting the image data; and performcharacter recognition processing to recognize a character in the imagerepresented by the image data, wherein the at least one processor isconfigured to perform a first processing in which: the correctionprocessing is performed to the image data of the first colorcorresponding to the first abnormal position in the image represented bythe image data; and the correction processing is performed, regardlessof presence or absence of the abnormal pixel of the second color, to theimage data of the second color corresponding to the first abnormalposition in the image represented by the image data, wherein the atleast one processor is configured to perform a second processing inwhich: the correction processing is performed to the image data of thefirst color corresponding to the first abnormal position in the imagerepresented by the image data; and the correction processing is notperformed, in a case where the abnormal pixel of the second color is notin the first abnormal position, to the image data of the second colorcorresponding to the first abnormal position in the image represented bythe image, and wherein the at least one processor is configured to:output the image obtained by the first processing in a case where thecharacter recognized by the character recognition processing to theimage obtained by the first processing and the character recognized bythe character recognition processing to the image obtained by the secondprocessing are the same, output the image obtained by the secondprocessing in a case where the character recognized by the characterrecognition processing to the image obtained by the first processing andthe character recognized by the character recognition processing to theimage obtained by the second processing are different from each other.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an image reading apparatus.

FIG. 2 is an explanatory diagram of an original detection sensor.

FIG. 3 is an exemplary diagram of a controller.

FIG. 4 is a configuration diagram of a reading image processing part.

FIG. 5A and FIG. 5B are exemplary diagrams representing a relationshipbetween a dust and a color line sensor.

FIG. 6 is an exemplary diagram of a digital value of each position inthe main scanning direction when there is a dust.

FIG. 7 is an explanatory diagram representing image processing performedby a full-color image correction part.

FIG. 8 is an explanatory diagram of a reading image before correction.

FIG. 9 is an explanatory diagram of the reading image after a full-colorstreak image correction.

FIG. 10 is an explanatory diagram of the reading image after asingle-color streak image correction.

FIG. 11 is a configuration diagram of a character recognition processingunit.

FIG. 12 is an explanatory diagram of a histogram.

FIG. 13A, FIG. 13B, and FIG. 13C are explanatory diagrams of thecharacter recognition processing with the streak image correction.

FIG. 14 is a flow chart representing image reading processing with astreak image correction.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments for carrying out the present invention will bedescribed with reference to the drawings.

<Configuration of Image Reading Apparatus>

FIG. 1 is a configuration explanatory diagram of an image readingapparatus of the present embodiment. The image reading apparatus 100includes an image reading unit 101 and an ADF 102. The image readingapparatus 100 is provided on a printer 200 to print an image on a sheet.The image reading apparatus 100 forms a part of an image formingapparatus 1, such as a copier or a multifunction apparatus, which formsan image on a sheet. The ADF 102 is arranged on an upper part of theimage reading unit 101. A platen 118 is provided on an ADF 102 sidesurface of the image reading unit 101. The ADF 102 is provided to beopenable and closable with respect to the platen 118.

The ADF 102 includes an original tray 104 on which an original bundle,which consists of one or more originals 103, is placed, a conveyancepath 130, and a discharge tray 117. The original 103 is conveyed one byone from the original tray 104 to the conveyance path 130, and isdischarged to the discharge tray 117. The original 103 is read by theimage reading unit 101 while it is conveyed along the conveyance path130. At a base end of the original tray 104, a pickup roller 106 forfeeding the original 103 from the original bundle to the conveyance path130 is arranged. In the original tray 104, a pair of width regulatingplates 105 are arranged at both ends in a direction (width direction)orthogonal to the conveyance direction of the original 103. The pair ofwidth regulating plates 105 regulates ends of the width direction of theoriginal bundle.

A separation roller 108 and a separation pad 107 are provided along theconveyance path 130 on a downstream side of the conveyance direction ofthe original 103 with respect to the pickup roller 106. The separationroller 108 and the separation pad 107 are arranged to face each otheracross the conveyance path 130. The separation roller 108 cooperateswith the separation pad 107 to separate the original 103 fed from theoriginal tray 104, from the top of the original bundle, to theconveyance path 130 by the pickup roller 106 one by one.

Along the conveyance path 130 on the downstream side of the conveyancedirection of the original 103 with respect to the separation roller 108,first and second registration rollers 109 and 110, first to fourthconveyance rollers 111, 112, 113, and 115, and a discharge roller 116are arranged. An original detection sensor 127 is arranged between thefirst conveyance roller 111 and the second conveyance roller 112. Thedetails of the original detection sensor 127 will be described later.The second conveyance roller 112 and the third conveyance roller 113 arepositioned such that a space between them is positioned above an uppersurface of the platen 118 of the image reading unit 101. The space is areading position of the image reading unit 101. A white guide member 114is arranged at a position facing the platen 118 across the conveyancepath 130.

A reading unit 129 is provided in a housing of the image reading unit101. The reading unit 129 includes lamps 119 and 120 as light sources,reflection mirrors 121, 122 and 123, an imaging lens 124, and a colorline sensor 125. The reflection mirrors 122 and 123 are arranged to facethe reflection mirror 121. The imaging lens 124 and the color linesensor 125 are arranged to face the reflection mirrors 122 and 123. Asignal processing board 126 is electrically connected to the color linesensor 125.

In the image reading apparatus 100 having the above configuration, theoriginal bundle placed on the original tray 104 of the ADF 102 isregulated in the width direction by the width regulating plate 105 tothereby prevent the original 103 from being conveyed diagonally. Thepickup roller 106 picks up the original 103 from the original bundle tofeed it to the conveyance path 130. The separation pad 107 and theseparation roller 108 cooperate to separate and convey the original 103one by one from the top of the original bundle.

The first registration roller 109 corrects the skew of the original P,which is separated into one and is conveyed by the separation roller108. The original 103 to which the skew correction has been performed isconveyed to the reading position by the second registration roller 110,the first conveyance roller 111, and the second conveyance roller 112.The original 103 is conveyed between the platen 118 and the white guidemember 114 at the reading position. The white guide member 114 pressesthe original 103 toward the platen 118 so that the original 103 passesthrough the ADF reading position while maintaining contact with theplaten 118. Further, the white guide member 114 is read by the readingunit 129 when the original 103 is not present at the reading position.Based on the reading result of reading the white guide member 114, it isdetermined whether or not a foreign matter such as dust or the like isadhering to the reading position. Moreover, the white guide member 114is used also for a shading correction.

The reading unit 129 performs a reading operation for the original 103passing through the reading position as follows. Start timing of thereading operation of the original 103 by the reading unit 129 iscontrolled according to the detection timing of the original 103 alongthe conveyance path 130 by the original detection sensor 127.

The lamps 119 and 120 of the reading unit 129 irradiate the original 103passing through the reading position with light. The reflection mirrors121, 122 and 123 reflect the light reflected by the original 103 towardthe imaging lens 124. The imaging lens 124 forms an image of thereflected light on a light receiving surface of the color line sensor125. the color line sensor 125 is equipped with two or more image pickupelements, such as CCD sensors or CMOS sensors. The reflected light formsan image on the light receiving surface of the image sensor. The colorline sensor 125 converts the received reflected light into an electricalsignal and transmits it to the signal processing board 126. Thedirection in which the plurality of image pickup elements are arrangedis a main scanning direction, and is orthogonal to the conveyancedirection of the original 103. The conveyance direction of the original103 is a sub-scanning direction.

The signal processing board 126 performs predetermined processing on theelectrical signal obtained from the color line sensor 125 and generatesimage data, which is a reading result of the original 103. The imagedata is a digital signal. The image data is transmitted to a printer 200from the image reading apparatus 100. In the case of copying processing,the printer 200 forms an image on the sheet based on the image data.

The original 103 to which reading processing is performed at the readingposition is conveyed to the third conveyance roller 113 by the secondconveyance roller 112. The original 103 is conveyed through the thirdconveyance roller 113, the fourth conveyance roller 115, and thedischarge roller 116 in this order, and the original 103 is dischargedto the discharge tray 117.

Manufacturing variations occur in the color line sensor for each imagepickup element (for each pixel). Further, it is not easy to make theirradiation light emitted from the lamps 119 and 120 uniform in the mainscanning direction. Therefore, even in a case where an image is readfrom the original 103 on which an image has been formed with a uniformimage density, the digital value of the image data, which is a readingresult, may vary depending on a position in the main scanning direction.

Shading correction is performed to suppress such variations.Specifically, the reading unit 129 reads the white guide member 114. Thewhite guide member 114 has a uniform white surface that is read by thereading unit 129. From a reading result of the white guide member 114, acorrection value is calculated so that the reading result (for example,a luminance value) in the main scanning direction becomes the samepredetermined value. With this correction value, the irradiation amountsof the lamps 119 and 120, the sensitivity variation of the image pickupelement, and the reading result of the image of the original 103 arecorrected, thus, the variation in manufacturing and the variation in theamount of light are corrected.

The reading unit 129 can also read an image of the original which ismanually placed on the platen 118 by the user. In this case, the lamps119 and 120 of the reading unit 129 and the reflection mirror 121 readthe original line by line while moving in the sub-scanning direction.

FIG. 2 is an explanatory diagram of an original detection sensor 127.The original detection sensor 127 includes an actuator 127 a and atransmissive sensor 301. The transmissive sensor 301 includes anirradiation unit 301 a and a light receiving unit 301 b.

The actuator 127 a collapses in the conveyance direction of the original103 when the original 103 is conveyed along the conveyance path 130 tothereby collide against the actuator 127 a. The actuator 127 a blocks,by collapsing in the conveyance direction of the original 103, anoptical path between the irradiation unit 301 a and the light receivingunit 301 b of the transmissive sensor 301. By blocking the optical pathbetween the irradiation unit 301 a and the light receiving unit 301 b,(for example, the amount of infrared light) the amount of light receivedby the light receiving unit 301 b from the irradiation unit 301 a willbe changed. The amount of light received by the light receiving unit 301b is converted into an electrical signal. The change in the amount oflight received by the light receiving unit 301 b corresponds to a changein the level of the electrical signal. From the change of the electricalsignal level, it is detected that the original 103 has reached thedetection position of the original detection sensor 127.

<Controller>

FIG. 3 is an explanatory diagram of a controller which controls anoperation of the image reading apparatus 100. The controller is built inthe image reading apparatus 100. In the present embodiment, thecontroller is comprised of a CPU (Central Processing Unit) 202, however,a semiconductor device such as an MPU or an ASIC may be used. The CPU202 controls the whole operation of the image reading apparatus 100 byexecuting a predetermined computer program.

The CPU 202 is in connection with an operation panel 201, the originaldetection sensor 127, a reading unit drive motor 204, an originalconveyance motor 205, the color line sensor 125, an AD converter 206, areading image processing part 207, a storage unit 208, and a characterrecognition processing part 209. The AD converter 206, the reading imageprocessing part 207, the storage unit 208, and the character recognitionprocessing part 209 are mounted on the signal processing board 126. TheCPU 202 can determine that the original 103 has reached the detectionposition of the original detection sensor 127 based on the change in thelevel of the electrical signal output from the original detection sensor127, as described above.

The operation panel 201 is a user interface including an input interfaceand an output interface. The input interface includes key buttons, atouch panel, and the like. The output interface includes a display, aspeaker, and the like. The CPU 202 controls the operation of the imagereading apparatus 100 in response to an instruction or the like inputfrom the input interface of the operation panel 201. The CPU 202 outputsinformation such as the status of the image reading apparatus 100 fromthe output interface of the operation panel 201. For example, the CPU202 displays the setting screen on the display when setting the readingconditions and the like to thereby accept the operation contents such assettings by the input interface.

The reading unit drive motor 204 is a drive source for moving thereading unit 129 in the sub-scanning direction under the control of theCPU 202. When reading an image from the original 103 placed on theplaten 118, the CPU 202 moves the reading unit 129 in the sub-scanningdirection by the reading unit drive motor 204.

The original conveyance motor 205 is a drive source for rotationallydriving various rollers arranged along the conveyance path 130. When theADF 102 is used to read the image of the original 103, the CPU 202controls the original conveyance motor 205 to feed the original 103 fromthe original tray 104.

The CPU 202 controls the operation of the color line sensor 125. Thecolor line sensor 125 converts the received reflected light into anelectrical signal and outputs it. The color line sensor 125 includes aplurality of line sensors to receive reflected light of a plurality ofcolors to read an image in a plurality of colors. In the presentembodiment, to receive the reflected light of three colors of R (red), G(green), and B (blue), the color line sensor 125 includes three linesensors each corresponding to respective color. The electrical signaloutput from the color line sensor 125 is an analog voltage of each colorcorresponding to R, G, and B.

The AD converter 206 obtains the analog voltage of each color from thecolor line sensor 125. The AD converter 206 converts the obtained analogvoltage of each color into reading data which is a digital value. Eachreading data converted from the analog voltage of each color by the ADconverter 206 is transmitted to the reading image processing part 207.The reading image processing part 207 performs predetermined processingon the reading data of each color to generate image data representingthe read image. The reading image processing part 207 stores the imagedata generated by reading the original 103 in the storage unit 208. Theimage data generated by reading the original 103 may be directlytransmitted to the printer 200 or another external device. The characterrecognition processing part 209 performs character recognitionprocessing to the image data stored in the storage unit 208 and stores acharacter recognition result in the storage unit 208. The characterrecognition processing part 209 determines a final output image databased on the character recognition result.

Although not shown, the printer 200 is also equipped with a controllerfor controlling the operation. The controller of the printer 200 cancommunicate with the CPU 202 of the image reading apparatus 100. Theoperation panel 201 is connected to the controller of the printer 200.The CPU 202 of the image reading apparatus 100 obtains the instructioninput from the operation panel 201 via the controller of the printer200. For example, an instruction for copying processing is input fromthe operation panel 201 to the controller of the printer 200. When thecontroller of the printer 200 obtains the copy processing instructionfrom the operation panel 201, the controller instructs the CPU 202 toperform the copying processing. According to this instruction, the CPU202 operates during the above copying processing.

<Reading Image Processing Part>

FIG. 4 is an explanatory configuration view of the reading imageprocessing part 207. The reading image processing part 207 includes astreak image detection unit 401, a position storing unit 402, afull-color image correction unit 403, and a single-color imagecorrection unit 404. In the following, a process, performed by thereading image processing part 207, of erasing the streak image generatedby the dust at the ADF reading position on the platen 118 is described.The reading image processing part 207 may have a function of performinganother processing on the reading image.

The streak image detection unit 401 obtains reading data of each colorconverted from the analog voltage of each color by the AD converter 206.Based on the reading data of each color obtained by reading the whiteguide member 114 by the color line sensor 125, the streak imagedetection unit 401 detects a position of the streak image generated bythe dust adhering to the platen 118. Here, the position of the streakimage corresponds to the position (pixel) in the main scanning directionat the ADF reading position on the platen 118. Hereinafter, the pixelcorresponding to the position of the streak image in the main scanningdirection is referred to as “abnormal pixel”.

FIGS. 5A and 5B are explanatory views of a relationship between the dust(foreign matter) at the reading position and the color line sensor 125.The color line sensor 125 of the present embodiment includes three linesensors (R sensor 502, G sensor 503, and B sensor 504) provided for eachcolor to receive the reflected light for each of the three colors. The Rsensor 502 includes a filter that transmits a red component of thereflected light to receive the red light. The G sensor 503 includes afilter that transmits a green component of the reflected light toreceive the green light. The B sensor 502 includes a filter thattransmits a blue component of the reflected light to receive the bluelight. The R sensor 502, the G sensor 503, and the B sensor 504 are theline sensors in which a plurality of the image pickup elements arearranged in the main scanning direction, respectively.

The reflected light reflected by the white guide member 114 or theoriginal 103 forms an image on a light receiving surface of the linesensor (R sensor 502, G sensor 503, and B sensor 504) of each color bythe imaging lens 124 through the reflection mirrors 121, 122, and 123.In FIG. 5A and FIG. 5B, a dust 501 is at a reading position of the Rsensor 502 and is not at a reading position of the G sensor 503 or the Bsensor 504. In FIG. 5A, the dust 501 is on the white guide member 114.In FIG. 5B, the dust 501 is on the platen 118. The optical path of thereflected light received by the R sensor 502 is shown by a dot-dashline, the optical path of the reflected light received by the G sensor503 is shown by a broken line, and the optical path of the reflectedlight received by the B sensor 504 is shown by a solid line.

Hereinafter, a detection method of the position of the abnormal pixel isexplained. First, the output of the color line sensor 125 when the colorline sensor 125 reads the white guide member 114 will be described.

FIG. 6 is an exemplary diagram of the reading data (digital value) ateach position in the main scanning direction based on the reading resultoutput from the color line sensor 125 when the dust 501 is on thereading position. In FIG. 6, a horizontal axis indicates each positionin the main scanning direction, and a vertical axis indicates thereading data (digital value). When the AD converter 206 outputs an 8-bitdigital value, the reading data when the analog voltage output from thecolor line sensor 125 is AD-converted is in a range of 0 to 255.

When the white guide member 114 is read after shading correction, thereading data is almost the same in the main scanning direction. However,for example, as shown in FIG. 5A, when the dust 501 is on the whiteguide member 114, the light emitted to the white guide member 114 isblocked by the dust 501 at the position where the dust 501 is located.Therefore, the reading data at this position is smaller than the otherpositions. The streak image detection unit 401 compares the reading datafor each position in the main scanning direction when the white guidemember 114 is read with a predetermined threshold value. As a result ofthe comparison, the streak image detection unit 401 determines a pixelcorresponding to a position where the reading data is smaller than apredetermined threshold value as a candidate for an abnormal pixel(abnormal pixel candidate).

Further, as shown in FIG. 5B, when the dust 501 is on the platen 118,the light emitted to the white guide member 114 is blocked by the dust501 at the position where the dust 501 is located. Therefore, thereading data at this position is smaller than the other positions. Thestreak image detection unit 401 compares the reading data for eachposition in the main scanning direction when the white guide member 114is read with a predetermined threshold value. As a result of thecomparison, the streak image detection unit 401 determines a pixelcorresponding to a position where the digital value is smaller than apredetermined threshold value as a candidate for an abnormal pixel(abnormal pixel candidate).

In the example of FIG. 6, the reading data when the white guide member114 is read is about 200. Therefore, for example, when the thresholdvalue is set to “180”, a pixel having the reading data lower than “180”can be determined as an abnormal pixel candidate. In the example of FIG.6, the pixels at the positions 1015 to 1020 in the main scanningdirection are determined to be abnormal pixel candidates.

Next, the output of the color line sensor 125 when the image of theoriginal 103 passing through the reading position 502 is read by thecolor line sensor 125 will be described.

As shown in FIG. 5A, when the dust 501 is on the white guide member 114and the original 103 passes over the platen 118, the dust 501 is hiddenby the original 103 when viewed from the color line sensor 125. As aresult, the streak image caused by the dust 501 does not appear in theimage representing the reading result of the original 103. That is, thevalues at the positions 1015 to 1020 in the main scanning direction inFIG. 6 do not become smaller than the predetermined threshold value dueto the dust 501.

As shown in FIG. 5B, when the dust 501 is on the platen 118 in the ADFreading position and the original P passes over the platen 118, theoriginal P is hidden by the dust 501 when viewed from the color linesensor 125. As a result, the streak image caused by the dust 501 appearsin the image representing the reading result of the original 103. Thatis, the values at the positions 1015 to 1020 in the main scanningdirection in FIG. 6 do not become smaller than the predeterminedthreshold value due to the dust 501. The streak image detection unit 401determines the pixel corresponding to the position where the readingdata is smaller than the predetermined threshold value as the candidatefor the abnormal pixel (abnormal pixel candidate).

The streak image detection unit 401 determines the abnormal pixel basedon the reading data obtained during a period of time from the start ofreading until the image of a predetermined length is read from the tipof the original 103. If the abnormal pixel candidates continuouslyappear in the sub-scanning direction at the same position in the mainscanning direction in the reading data of the period, the streak imagedetection unit 401 determines, among the abnormal pixel candidate, thepixel at the position in the main scanning direction as the abnormalpixel. That is, if the streak image appears continuously before andafter the original 103 reaches the reading position, the streak imagedetection unit 401 determines, in the streak image, the pixel at theposition in the main scanning direction as the abnormal pixel. Thestreak image detection unit 401 generates information for each color(red streak image information, green streak image information, and bluestreak image information) which indicates the position of the abnormalpixel. Then, the streak image detection unit 401 stores the same in theposition storing unit 402.

The streak image information (position information) stored in theposition storing unit 402 is read by the full-color image correctionunit 403 and the single-color image correction unit 404. The full-colorimage correction unit 403 and the single-color image correction unit 404performs, based on information obtained from the position storing unit402, linear interpolation of the read data corresponding to the positionof the streak image (the target pixel) to thereby correct (remove) thestreak image caused by the foreign matter. The reading image processingpart 207 stores image data obtained by correcting the reading data inthe storage unit 208. A method of detecting the abnormal pixel is notlimited to the method described above, but can be any known method.

FIG. 7 is an explanatory diagram of image processing of the full-colorimage correction unit 403. The position storing unit 402 stores thefull-color streak image information (red streak image information, greenstreak image information, and blue streak image information). In thefull-color streak image information, as to each of the R sensor 502, Gsensor 503, and B sensor 504, “1” is set for the position in the mainscanning direction (position of an abnormal pixel) at which it isdetermined that the streak image has occurred. Further, “0” is set forthe position in the main scanning direction at which it is determinedthat the streak image has not occurred. Due to the full-color streakimage information, it is possible to know which position in the mainscanning direction the streak image occurs. The streak image correctionis performed based on the streak image information.

In the red streak image information in FIG. 7, the value of the targetpixel (target position) is “1”, which indicates that the streak imagehas occurred at the target pixel. As to the positions N−3, N−2, N−1,N+1, N+2, and N+3 around the target pixel in the main scanningdirection, the red streak image information is “0”. This indicates thatthe streak image has not occurred. The reading data of red color of thetarget pixel is “80”, which is smaller than the reading data of thepixel which is at a position around the target pixel.

The full-color image correction unit 403 first identifies the positionof the streak image (abnormal pixel) based on the red streak imageinformation obtained from the position storing unit 402. Next, thefull-color image correction unit 403 refers to the reading data of theposition adjacent to the specified position of the streak image in themain scanning direction to interpolate the digital value of the positionof the streak image linearly. By performing the linear interpolation,the streak image is removed.

In the example of R sensor 502, both the position N−1 and the positionN+1 are adjacent to the target pixel at which the streak image hasoccurred. The reading data of position N−1 is “190”, and the readingdata of position N−1 is “192”. Assuming that the reading data of thetarget pixel is D [N], the reading data of the adjacent pixels are D[N−1] and D [N+1], and the corrected (after linear interpolation)reading data of the target pixel is D [N]′, the reading data D [N]′ isexpressed by the formula (1).

D[N]′=D[N−1]+(D[N+1]−D[N−1])/2  (1)

D[N]′=190+(192−190)/2=191

Therefore, the reading data D [N]′ of the target pixel after linearinterpolation is “191”. By converting the reading data “80” of thetarget pixel before correction to “191” as described above, the streakimage correction is completed.

The full-color image correction unit 403 performs the streak imagecorrection processing at the position (pixel) in the main scanningdirection at which the streak image has occurred as described above.Even in a case where the abnormal pixel (the streak image) is detectedonly at the reading position of the R sensor 502, the full-color imagecorrection unit 403 performs the same streak image correction processingon the reading data of the same position (pixel) in the main scanningdirection obtained from the reading results of the G sensor 503 and theB sensor 504. As a result, the reading data “185” of the target pixel inthe green streak image information is corrected to “191”. The readingdata “185” of the target pixel in the blue streak image information iscorrected to “191”.

The single-color image correction unit 404 selects, based on thefull-color streak image information obtained from the position storingunit 402, a color to which the streak image correction is performed.When the streak image occurs only in the ADF reading position of the Rsensor 502 as shown in FIG. 7, the reading data of the red color becomesa smaller value. Therefore, the streak image of the green component andthe blue component is formed in the read image. The single-color imagecorrection unit 404 corrects only for the color for which the streakimage is detected. The correction is performed by the linearinterpolation as in the full-color image correction unit 403.

The difference after the corrections between the full-color streak imagecorrection and the single-color streak image correction will bedescribed with reference to FIGS. 8 to 10. FIG. 8 shows a state beforethe correction. FIG. 9 shows a state after correction by the full-colorimage correction unit 403. FIG. 10 shows a state after correction by thesingle-color image correction unit 404.

FIG. 8 shows an example of the reading image when the dust is on thereading position of the R sensor 502. The reading data of the printedportion is black (R, G, B)=(0,0,0). Since the reading data of the redcolor becomes smaller due to the dust, the streak image (color streak)(R, G, B)=(0,255,255) has occurred.

The full-color image correction unit 403 performs the streak imagecorrection for each color component of full-color (R, G, B). When thefull-color image correction unit 403 performs the streak imagecorrection based on the equation (1) for the full-color streak imageinformation as shown in FIG. 8, the result shown in FIG. 9 is obtained.That is, the streak image (color streak) of (R, G, B)=(0, 255, 255) andthe printed portion of (R, G, B)=(0, 0, 0) are corrected, and thereading data of each position becomes (R, G, B)=(255, 255, 255). In thisway, the printed portion may be erased by performing the streak imagecorrection of the full-color in a case where the streak image overlapsthe printed portion.

The single-color image correction unit 404 performs the streak imagecorrection only for the red color for which the streak image isdetected. When the single-color image correction unit 404 performs thestreak image correction based on the formula (1) for the red streakimage information as shown in FIG. 8, the result shown in FIG. 10 isobtained. That is, the streak image (color streak) of (R, G, B)=(0, 255,255) is removed, however, the printed portion becomes (R, G, B)=(255, 0,0). In this way, by performing the single-color streak image correction,the color of the printed portion changes and the printed portion becomeschromatic color, however, the printed portion is not erased in a casewhere the streak image overlaps the printed portion.

The reading image processing part 207 stores the two reading data aftercorrecting the streak image as described above as image data in thestorage unit 208. Although a configuration having the full-color imagecorrection unit 403 and the single-color image correction unit 404 isdescribed in the present embodiment, the two units may be combined toform a streak image correction unit. When the single streak imagecorrection unit is used, the reading image processing part 207sequentially stores the image data in which the single-color streakimage correction has been performed and the image data in which thefull-color streak image correction has been performed in the storageunit 208.

<Character Recognition Comparison>

The character recognition processing part 209 performs the characterrecognition processing for each of the image data, which are stored inthe storage unit 208, i.e., the image data after the full-color streakimage correction and the image data after the single-color streak imagecorrection. The character recognition processing part 209 compares eachcharacter recognition result and determines the image data to be finallyoutput. Hereinafter, the image data after the full-color streak imagecorrection is referred to as “first image data”, and the image dataafter the single-color streak image correction is referred to as “secondimage data”.

FIG. 11 is a configuration explanatory diagram of the characterrecognition processing part 209. The character recognition processingpart 209 includes a binarization processing unit 1101, a characterdetermination unit 1102, and a character detection result comparisonunit 1103.

The binarization processing unit 1101 reads the first image data fromthe storage unit 208 and performs the binarization processing on thefirst image data. The binarization processing unit 1101 converts thefirst image data from RGB color space to YCbCr color space for thebinarization processing. The binarization processing unit 1101 obtains ahistogram by plotting the number of pixels of the luminance signal Y(yellow) for each luminance value from 0 to 255 from the first imagedata converted into the YCbCr color space. FIG. 12 is an exemplarydiagram of such a histogram. The binarization processing unit 1101 sets,for the histogram, a threshold value so as to separate a bright signaland a dark signal. For example, the binarization processing unit 1101binarizes the first image data by setting “0” for a luminance valuebelow the threshold value and setting “255” for a luminance value abovethe threshold value to “255”. The binarization processing unit 1101transmits the binarized first image data to the character determinationunit 1102. The character determination unit 1102 extracts a characterfrom the binarized first image data obtained from the binarizationprocessing unit 1101 by a character recognition process to store acharacter code of the extracted character in the storage unit 208. Thecharacter recognition process is performed by, for example, an OCR(Optical Character Recognition) process.

The binarization processing unit 1101 and the character determinationunit 1102 also perform the binarization processing and the characterrecognition process for the second image data, as in the first imagedata. Thereby, the character determination unit 1102 stores thecharacter code of the character extracted from the second image data inthe storage unit 208.

The binarization method is not limited to the above method as long asthe RGB image is binarized and converted into data that can berecognized as characters. Further, the character recognition method maybe any method as long as the characters can be determined.

The character detection result comparison unit 1103 compares thecharacter code obtained from the first image data with the charactercode obtained from the second image data. FIGS. 13A to 13C areexplanatory diagrams of character recognition results. FIG. 13A is adiagram in a case where the streak image generated by the dust adheringto the reading position of the R sensor 502 affects a part of acharacter “B” in a character string “ABC”. In a case where such areading image is corrected by the full-color image correction unit 403to perform the character recognition process, the character string maybe erroneously recognized as “A3C”, as shown in FIG. 13B. In a casewhere the reading image is corrected by the single-color imagecorrection unit 404 and then the character recognition is performed, thecolor of the character changes and becomes chromatic color, however, asshown in FIG. 13C, the character string “ABC” can be recognized.

The character detection result comparison unit 1103 compares thecharacter code obtained from the first image data with the charactercode obtained from the second image data. Based on the results, itdetermines whether the character codes match or not. The characterdetection result comparison unit 1103 transmits the detection result tothe CPU 202. In a case where the character codes match, the CPU 202selects, as the image data of the final output image, the first imagedata to which the full-color streak image correction has been performedby the full-color image correction unit 403. In a case where thecharacter codes do not match, the CPU 202 selects, as the image data ofthe final output image, the second image data to which the single-colorstreak image correction has been performed by the single-color imagecorrection unit 404.

<Image Reading Processing>

FIG. 14 is a flow chart representing the image reading processingincluding the streak image correction by the image reading apparatus 100having the above configuration. The image reading apparatus 100 canoperate in two reading modes, e.g., a first reading mode and a secondreading mode. The first reading mode is a reading mode in which thestreak image correction of full-color is performed by suppressing achange in color, for example, when reading an image for copy output. Thesecond reading mode is a reading mode in which the streak imagecorrection is performed while avoiding the loss of characterinformation, as in the case of reading an image such as a form.

The CPU 202 determines whether or not the user pressed the image readingstart button provided on the operation panel 201 (STEP S101). The CPU202 makes the above determination based on whether or not a signaltransmitted from the operation panel 201 is obtained when the imagereading start button is pressed. When the image reading start button isnot pressed (STEP S101: N), the CPU 202 determines whether or not thepredetermined time has elapsed without pressing the image reading startbutton and the timeout has occurred (STEP S102). If the timeout has notoccurred (STEP S102: N), the CPU 202 returns to the process of STEP S101and determines whether the image reading start button has been pressedagain. When the time-out has occurred (STEP S102: Y), the CPU 202controls the image reading apparatus 100 to enter a sleep state in whichthe power consumption is lower than usual, and ends the processing (STEPS103).

In a case where the image reading start button is pressed (STEP S101:Y), the CPU 202 determines whether or not the second reading mode isselected (STEP S104). The reading mode is set through the operationpanel 201, for example, before the image reading start button ispressed. For example, the user sets the first reading mode at the timeof copying, and sets the second reading mode at the time of digitizing aform.

In a case where the second reading mode is selected (STEP S104: Y), theCPU 202 sets the image reading apparatus 100 (color line sensor 125) toperform the image reading in color mode (STEP S105). Then, the CPU 202drives the original conveyance motor 205 to start feeding the original103 (STEP S106). The CPU 202 turns on the lamps 119 and 120 when theoriginal detection sensor 127 detects the original 103 during conveyingthe same, then, the CPU 202 starts the reading operation using the colorline sensor 125 (STEP S107). The reading operation is started before theoriginal 103 reaches the reading position. That is, the color linesensor 125 reads the white guide member 114 before the original 103reaches the reading position, then, the color line sensor 125 reads theimage of the original 103 when the original reaches the readingposition. The CPU 202 detects the above-mentioned streak image by thereading image processing part 207 based on the respective reading dataof the white guide member 114 and the original 103 (STEP S108). By thestreak image detection, all color the streak image information is storedin the position storing unit 402.

When the image of the original 103 is read, as to the reading data ofthe original 103, the CPU 202 performs the single-color streak imagecorrection for only the color for which the streak image is detected(STEP S109). This correction is performed by using the single-colorimage correction unit 404 and based on the full-color streak imageinformation stored in the position storing unit 402. The reading dataafter the single-color streak image correction is stored in the storageunit 208 as the second image data. Further, as to the reading data ofthe original 103, the CPU 202 performs the full-color streak imagecorrection for full-color for which the streak image is detected (STEPS110). This correction is performed by using the full-color imagecorrection unit 403 and based on the full-color streak image informationstored in the position storing unit 402. The reading data after thefull-color streak image correction is stored in the storage unit 208 asthe first image data.

The CPU 202 performs the character recognition process of the secondimage data generated in the process of S109 and the first image datagenerated in the process of STEP S110 by the character recognitionprocessing part 209 (STEP S111). As a result of the characterrecognition process, the character codes of the second image data andthe first image data are stored in the storage unit 208, respectively.The CPU 202 compares the character code obtained from the second imagedata with the character code obtained from the first image data by thecharacter detection result comparison unit 1103 (STEP S112).

As a result of the comparison, when the character codes are differentfrom each other (STEP S112: Y), the CPU 202 determines the second imagedata generated by the single-color streak image correction as the imagedata to be finally output to output the same (STEP S113). As a result ofthe comparison, when the character codes are the same (STEP S112: N),the CPU 202 determines the first image data generated by the full-colorstreak image correction as the image data to be finally output andoutputs the same (STEP S114).

After outputting the image data, the CPU 202 determines whether or notthe original 103 from which the image is read is the last original (STEPS115). For example, a sensor for detecting the presence or absence ofthe original on the original tray 104 is provided in the original tray,and the determination of the last original is performed based on thedetection result of this sensor. In a case where the read original 103is not the last original (STEP S115: N), the CPU 202 returns to theprocess of STEP S106 and feeds the next original to read the image. Whenthe original 103 is the last original (STEP S115: Y), the CPU 202 endsthe process.

When the second reading mode is not selected as the reading mode (STEPS104: N), the CPU 202 operates in the first reading mode. In the firstreading mode, setting of the color/monochrome reading is performed by auser. The CPU 202 feeds the original 103 to read an image from theoriginal 103 being conveyed (STEP S116, STEP S117). The CPU 202 detectsthe streak image based on the respective reading data of the white guidemember 114 and the original 103 (STEP S108). The processing from thefeeding start of the original 103 to the detection of the streak imageis the same as the process of STEPs S106-S108.

The CPU 202 performs the full-color streak image correction by thefull-color image correction unit 403 after reading the image of theoriginal (STEP S119). The full-color streak image correction process isthe same as the process of STEP S110. In the first reading mode, thestreak image correction for all colors is always performed to preventthe achromatic original image from changing to the chromatic colorreading image. The CPU 202 determines the second image data generated bythe full-color streak image correction as the image data to be finallyoutput and outputs the same (STEP S120). The printer 200 forms an imageon the sheet based on the output image data.

After that, the CPU 202 determines whether or not the original 103 fromwhich the image is read is the last original (STEP S121). In a casewhere the read original 103 is not the last original (STEP S121: N), theCPU 202 returns to the processing of STEP S116 and feeds the nextoriginal to read the image. In a case where the original 103 is the lastoriginal (STEP S121: Y), the CPU 202 ends the process.

The image reading apparatus 100 described above can appropriatelycorrect the streak image caused by the foreign matter even when theforeign matter such as the dust is on the platen 118. As a result, theimage reading apparatus 100 can perform image reading with reducing riskof rewriting characters and suppressing unnecessary coloring of the readimage. In this way, the streak image can be appropriately corrected.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2021-036929, filed Mar. 9, 2021, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image reading apparatus comprising: aconveyance unit configured to convey an original; a reading unitcomprising a reading sensor, the reading sensor having a light receivingelement to receive light of a first color and a light receiving elementto receive light of a second color that is different from the firstcolor, wherein the reading unit is configured to read an image of theoriginal conveyed by the conveyance unit by using the reading sensor togenerate image data which represents a reading result of the readingunit; at least one processor configured to: determine a first abnormalposition that is a position in a first direction of an abnormal pixel ofthe first color in an image represented by the image data, wherein, inthe image represented by the image data, the first direction is adirection which intersects a second direction corresponding to aconveyance direction in which the original is conveyed; determine asecond abnormal position that is a position in the first direction of anabnormal pixel of the second color in the image represented by the imagedata; perform correction processing for removing the streak image bycorrecting the image data; and perform character recognition processingto recognize a character in the image represented by the image data,wherein the at least one processor is configured to perform a firstprocessing in which: the correction processing is performed to the imagedata of the first color corresponding to the first abnormal position inthe image represented by the image data; and the correction processingis performed, regardless of presence or absence of the abnormal pixel ofthe second color, to the image data of the second color corresponding tothe first abnormal position in the image represented by the image data,wherein the at least one processor is configured to perform a secondprocessing in which: the correction processing is performed to the imagedata of the first color corresponding to the first abnormal position inthe image represented by the image data; and the correction processingis not performed, in a case where the abnormal pixel of the second coloris not in the first abnormal position, to the image data of the secondcolor corresponding to the first abnormal position in the imagerepresented by the image, and wherein the at least one processor isconfigured to: output an image obtained by the first processing in acase where the character recognized by the character recognitionprocessing to the image obtained by the first processing and thecharacter recognized by the character recognition processing to theimage obtained by the second processing are the same, output an imageobtained by the second processing in a case where the characterrecognized by the character recognition processing to the image obtainedby the first processing and the character recognized by the characterrecognition processing to the image obtained by the second processingare different from each other.
 2. The image reading apparatus accordingto claim 1, wherein the at least one processor is configured to binarizeimage data corresponding to the image obtained by the first processingand image data corresponding to the image obtained by the secondprocessing, respectively, and wherein the at least one processor isconfigured to recognize a character in the binarized image data.
 3. Theimage reading apparatus according to claim 1, wherein the at least oneprocessor is configured to recognize the character by an OCR.
 4. Theimage reading apparatus according to claim 1, wherein the reading unitis configured to read the image of the original passing through areading position on a transparent member through the transparent member;wherein the image reading apparatus includes a white member arranged ata side opposite to the reading unit with respect to the transparentmember at the reading position; and wherein the at least one processoris configured to determine the first abnormal position and the secondabnormal position based on a result of reading the white member by thereading unit and a result of reading the image of the original.
 5. Theimage reading apparatus according to claim 1, wherein the correctionprocessing is processing of correcting the image data to be corrected byusing image data corresponding to a pixel adjacent to a pixelcorresponding to the image data to be corrected in the first direction.